Restructure monitor enumeration

This way is both kinder on event-based enumeration and less work to
unwind allocations for when properly implementing GLFW_OUT_OF_MEMORY.

src/cocoa_window.m

@@ -340,7 +340,7 @@ static const NSRange kEmptyRange = { NSNotFound, 0 };
 
 - (void)applicationDidChangeScreenParameters:(NSNotification *) notification
 {
-    _glfwInputMonitorChange();
+    _glfwPollMonitorsNS();
 }
 
 - (void)applicationDidFinishLaunching:(NSNotification *)notification